Ultrasonic energy has been taught as useful for fiber liberation, disintegration, and the like and for other purposes in the making of paper, paperboard, and like natural cellulosic-fiber materials. However, conventionally when fabricating such materials into various items of manufacture, such as corrugated board, laminated paper products, convoluted cardboard tubing, paper bags, and numerous other useful items, the fabrication methods and techniques depend on adhesive bonding of the materials. With the just-mentioned materials and a starch adhesive bonding thereof, it is believed to be unknown to employ ultrasonic energy as taught herein.
Some studies have been made of the effect of ultrasonic energy on starch and starch paste. Illustrative thereof are teachings of: "Sonification Effect on Potato Starch and Sweet Potato Powder", A. Azhar and K. Hamdy, Journal of Food Science, Vol. 44 (1979) p. 801-804; "The Effects of Ultrasound on Starch Grains", M. DeGrois, D. Gallant, P. Baldo, and Guilbot, Ultrasonics, May 1974, p. 129-131; and "Starch and Its Derivatives", J. A. Radley, Vol. One, 3rd Edition, (1953), paragraph bridging p. 112-113. In general, those teachings report the effect of ultrasound on starch to be starch degradation and deterioration.
Illustrative of the present-day status of the making of corrugated board is a descriptive review in Chapter 26 "Corrugating" by A. J. Didominicis and G. H. Klein in the text of "Pulp and Paper Chemistry and Chemical Technology", Vol. IV, Third Edition, (1983), James P. Casey--Editor, John Wiley & Sons.
As taught in the just-mentioned text, in corrugated board production, starch adhesive is used to bond the liner(s) to the fluted medium. In a typical adhesive formulation, a major portion of the starch is uncooked to maintain reasonable viscosity levels prior to application to the tips of the flutes. Heat is applied to the starch mixture to achieve gelatinization of the starch so that it acts as an adhesive. Typically, the heat is applied to the starch during passage between pressure rolls by thermal conduction through the preheated fluted medium contacting a heated roll and/or by thermal conduction through the preheated liner contacting a heated roll. Problems with this process include the following: (1) poor quality low strength, bonds frequently result from non-uniform heating of the adhesive; (2) non-uniform heating of the liner or fluted medium often distorts the resultant corrugated board; and (3) inefficient use of thermal energy in heating those portions of the liner and fluted medium that do not require bonding.
The invention described herein minimizes these problems and achieves better bonding at higher production rates while reducing energy consumption.